As a technique for increasing the capacity of a semiconductor power converter, a multiplexed system using a transformer for converter is known. However, use of a transformer for converter may increase the weight and volume of an electrical power converter, and may cause DC biased magnetization when a system is disturbed. Therefore, there are attempts for practical use of a multilevel converter for realizing capacity increase and waveform improvement in a converter without using a transformer.
A multilevel converter is proposed which has a circuit configuration in which multiple converter cells for generating AC voltage on AC voltage terminals U, V, and W and DC voltage on DC voltage terminals P and N through ON/OFF control for a semiconductor switching element are connected in series between the AC voltage terminals U, V, and W and the DC voltage terminals P and N (for example, non-Patent Document 1).
A multilevel converter is proposed in which reactors are added between the AC voltage terminals U, V, and W and the DC voltage terminal P and between the AC voltage terminals U, V, and W and the DC voltage terminal N in the circuit configuration of the electrical power converter of non-Patent Document 1 (for example, non-Patent Document 2). Further, a multilevel converter is proposed which has reactors such that the reactor connected at the positive side and the reactor connected at the negative side are magnetically coupled with each other (for example, non-Patent Document 3).